<p>
  directive works!
</p>
<h2 yellowBg>
如何建立一个自定义指令
</h2 >

<h2>动态的变化颜色</h2>
<p>
  <input type="radio" name="colors" (click)="color='red'" />红色
  <input type="radio" name="colors" (click)="color='green'" />绿色
</p>
<div  [YellowBg2]="color">变化的颜色</div>
<h2>
  响应用户操作
</h2>
<div [YellowBg3]="'red'">响应</div>

